WASHINGTON — The Trump administration, setting the stage to move forward with one of its most consequential climate-policy rollbacks, announced Thursday that it had decided to scrap negotiations with California over the president’s plan to undo Obama-era fuel efficiency standards for cars and light trucks.

The move makes a protracted legal battle almost certain. At the heart of the talks was California’s longstanding right to opt out of national auto emissions rules and set its own tailpipe standards. State officials have vowed to sue to protect that authority if the administration tries to impose weaker federal standards on California and the dozen states that follow its lead.

Xavier Becerra, the California attorney general, said Thursday the state was “prepared to defend our national Clean Car standards even if the Trump administration intends to go AWOL.”

Under rules established by President Barack Obama’s administration to cut planet-warming greenhouse gas emissions from tailpipes, national fuel economy standards would nearly double by 2025. The Trump administration said in August that it intended to freeze that measure after 2021, when new cars must average around 30 miles a gallon. It also said it would challenge the right of California and the states that follow its lead to set their own rules.

There appears to have been very little movement in the negotiations since they began almost a year ago, and both sides on Thursday accused the other of negotiating in bad faith.

“Despite the administration’s best efforts to reach a common-sense solution, it is time to acknowledge that CARB has failed to put forward a productive alternative,” a White House statement said, referring to the California Air Resources Board, the state’s clean air regulator. “Accordingly, the administration is moving forward to finalize a rule later this year with the goal of promoting safer, cleaner and more affordable vehicles.”

Stanley Young, a spokesman for the air resources board, said meetings between the sides had been held but “were always at a superficial level, with no effort to engage in a conversation.”

Mandy Gunasekara, who served as principal deputy assistant administrator in the Environmental Protection Agency’s Office of Air and Radiation before leaving this month to start a private consulting business, and who was involved in the talks, said that California had put forward only one counterproposal: a plan to delay implementation of the fuel economy rules by one year. Trump officials saw that as a nonstarter.

“Looking at it now, it seems they were more interested in stalling the progress of the conversation than actually working to make a deal,” Ms. Gunasekara said.

The decision to abandon talks does not necessarily mean that a final proposal from the administration is imminent. The E.P.A. had planned to complete the rollback proposal by the end of March, but the partial government shutdown early this year set that target back to May or June, agency officials said.

Automakers, who fear that competing rules will bring chaos to the domestic auto industry, called for continued talks.

“We continue to believe there is a middle-ground solution that supports the goals of the administration, state of California, as well as automakers,” said John Bozzella, chief executive of Global Automakers, which represents automakers and parts suppliers with operations in the United States.

“We always knew achieving one national program would be challenging,” said Gloria Bergquist, a vice president at the Alliance of Automobile Manufacturers, which represents the country’s biggest automakers. But a compromise “is worth striving for,” she said. “We encourage everyone to keep focusing on how we get there.”

The announcement comes amid fast-deteriorating relations between Washington and California.

In recent weeks the Trump administration has said it was terminating a $929 million federal grant for the state’s struggling high-speed rail project, and the Transportation Department said it was exploring legal options to claw back $2.5 billion that had already been spent. President Trump has also threatened to cut off federal funding for wildfire relief after devastating blazes that killed 89 people.

Mr. Trump also lashed out on Twitter when 16 states sued over his decision to declare a national emergency in order to obtain funding for a border wall, writing that California, “the state that has wasted billions of dollars on their out of control Fast Train, with no hope of completion, seems in charge!”

Lisa Friedman reported from Washington and Hiroko Tabuchi from New York.

Lisa Friedman reports on climate and environmental policy in Washington. A former editor at Climatewire, she has covered nine international climate talks. @LFFriedman

Hiroko Tabuchi is a climate reporter. She joined The Times in 2008, and was part of the team awarded the 2013 Pulitzer Prize for Explanatory Reporting. She previously wrote about Japanese economics, business and technology from Tokyo. @HirokoTabuchi•Facebook

A version of this article appears in print on , on Page A16 of the New York edition with the headline: Administration Ends Clean Air Talks With California. Order Reprints | Today’s Paper | Subscribe